The goal of this proposal is to determine if ADAR proteins edit or affect the processing of micro RNAs (miRNAs) in the model organism C. elegans. It has been shown in a single instance in mouse that editing of a mature miRNA can redirect the miRNA to target new mRNAs and therefore alter gene silencing. ADARs have also been observed in a handful of examples to inhibit multiple steps in the biogenesis of human or mouse miRNAs in vitro. However, no unbiased global approach has been performed in any organism to study ADAR editing of miRNAs or ADARs'effect on miRNA processing;only candidate approaches have been used in previous studies of miRNAs. Furthermore, it has not even been tested whether ADARs edit or affect processing of miRNAs in C. elegans. As research continues, it is clear that miRNAs are essential for gene regulation in all metazoans. To fully understand miRNA-mediated gene regulation, it is essential to understand how ADARs affect miRNAs. I propose to do an in- depth analysis of miRNAs in C. elegans strains that lack ADARs, to determine if ADARs affect miRNA levels and/or edit miRNAs. C. elegans provide an ideal system to study ADARs effects on miRNAs, as ADAR null vertebrate models are lethal, while ADAR null worms are viable. These ADAR null worms are a powerful tool, as real editing sites can be distinguished from sequencing errors by comparing sequencing reads from wild-type and ADAR null worms. Furthermore, the biological consequences of ADARs'effects on miRNAs, such as down-stream changes in gene expression, can more easily be identified and studied in ADAR null worms. Aims: Aim 1 To identify ADAR editing sites in miRNAs Aim 2 To determine how ADARs affect miRNA processing Aim 3 To determine if there are biological consequences due to ADARs'effects on miRNAs PUBLIC HEALTH RELEVANCE: Extensive research has shown that small RNAs are key for development in a plethora of organisms and nearly every studied tissue, from heart to the nervous system. Altered levels of small RNAs have been linked to cancer, in various systems, indicating that processes that control small RNA levels also affect cancer. I plan to identify if the RNA editing proteins ADARs affect small RNA levels and/or function, and would therefore indicate that research of ADARs'affect on small RNAs would have strong implications for cancer prevention.